The TDI Understanding Nitrox Student Manual is the text-book literary assistant to the TDI Understanding Nitrox certification course. In many respects, nitrox is just a tool that can make your diving more enjoyable. Similar to an additional piece of equipment, once you have completed this TDI course and logged your first few nitrox dives, you will understand what a valuable tool it is. Nitrox will add useful options and flexibility to your dive planning and execution.